FIG. 1 is a schematic diagram illustrating a prior art mammography machine (100). The mammography machine (100) has an x-ray source (103), a beam limiting device (104) and a support platform (106) for positioning a part of the patient's body, which in this case is the breast (102). The mammography machine (100) also includes the x-ray sensor (101) and the CCD detector (105). The x-ray sensor (101) is attached to the CCD detector (105) and moves along the track (107). The x-ray sensor (101) is used to determine the quantity of energy passing through the breast (102). The CCD detector (105) is used to create an image for diagnostic purposes. In other mammography machines, the CCD sensor (105) is not utilized and the image is made on a film.
The x-ray sensor (101) is also used in automatic exposure controls to control the time of exposure of an x-ray source (103) and, when film is used, to provide the proper optical density on the film. This type of sensor might include solid state devices, ionization chambers or photo-multiplier tubes.
In several applications, a narrow x-ray beam (108) is scanned across the breast (102). A slot scanning x-ray procedure is one such application. In slot scanning applications, a beam limiting device (104) is swept to produce the narrow scanning x-ray beam (108). It is desirable to know the location of the scanning x-ray beam (108) as well as its intensity.
To obtain an x-ray exposure, the beam limiting device (104), the x-ray sensor (101) and the CCD detector (102) traverse the breast (102) at a constant velocity. Thus the narrow x-ray beam (108) scans across the breast (102) from right to left as indicated by the arrow (121). During exposure of the breast (102), the CCD detector (105) and sensor (101) move along track (107) from right to left as indicated by the arrows (111).
FIG. 2 is an enlargement of the lower portion of the x-ray machine shown in FIG. 1, detailing the x-ray sensor (101), the CCD detector (105) and the track (107) used for movement. FIG. 2 also shows arrows (111) which indicate the direction of movement along the track (107).
The movement of the sensor (101) and detector (105) along track (107) is aligned with the scanning narrow x-ray beam (108). The x-ray beam (108) is scanned by a servo-positioning motor (110) which moves the beam limiting device (104). FIG. 3 is an enlargement of the upper portion of the x-ray machine shown in FIG 1, detailing the servo-positioning motor (110) and the beam limiting device (104).
Slot scanning applications described in the current literature all rely on mechanical interfaces for moving the scanning x-ray beam (108), sensor (101) and the detector (105). These interfaces are complex and costly and are prone to alignment problems which reduce the quality of the produced image.
In short, the quality of a slot scanning system is a function of the location of the scanning x-ray beam (108) as well as its intensity. It is a function of the accuracy of synchronously moving the beam limiting device (104), the sensor (101) and the detector (105) in the same direction (111) across the breast (102).
In view of the foregoing, it is an object of the invention to provide an automatic position control system for an x-ray machine such as a mammography machine in which the x-ray beam and x-ray sensor synchronously scan across the breast or other part of the patient's body.
It is a principal object of the invention to provide an x-ray machine especially for mammography which includes an automatic position control system for maintaining the position of an x-ray beam with respect to an x-ray sensor without cumbersome mechanical interfaces.
It is also an object of the invention to provide an x-ray sensor for use in such a position control system, which sensor outputs a signal indicative of the position of a narrow x-ray beam.